Current apparatus and methods for attaching structural attachments to a structural stringer of an airplane exist in the art. Airplane stringers extend longitudinally along the fuselage of an aircraft and attach to the aircraft skin and transverse frame members. Airplane stringers also extend outwardly along the wing of an airplane and attach to the aircraft skin of the wing and transverse wing frame members.
FIG. 1 (Prior Art) is a prior art figure showing a portion of an airplane fuselage including skin 101 supported on a plurality of stringers, such as stringer 102. As depicted, the stringers are also connected to an airplane frame member 103. In manufacturing, stringers are often rolled from sheets of aluminum and vary in thickness and dimensions. Stringers are commonly formed into hat-shaped, S-shaped or Z-shaped cross-sections. The stringer 102, for example, depicted in FIG. 1 is a hat-shaped stringer. The top of the hat for stringer 102 is attached to the skin 101, and the two flanges of the stringer 102 are attached to the transverse frame member 103.
Stringer clips are attached to stringers and used to hold non-structural elements, such as wire bundles, air conditioning conduits, hydraulic lines, electronic equipment and other desired interior elements of an aircraft. One prior technique for attaching stringer clips to aircraft stringers was to drill holes through stringer flanges in order to attach the stringer clips. This technique, however, has the disadvantage of causing removal of protective coatings, increased stresses, and stress corrosion around the drill holes. It is appreciated that the stringers must remain in place during various gravitational stresses, vibrational stresses, and other forces experienced by an aircraft. A modern jet aircraft can use thousands of stringer clips, and it is desirable for these stringer clips to have minimal or no impact on the structural integrity of the stringers and the aircraft.
An example stringer clip is described in U.S. Pat. No. 4,896,851. The disclosed stringer clip provides a solution that uses an adjustable flexible strap to secure the stringer clip in place. An attachment mechanism for interior aircraft elements is also located centrally with respect to the strap. While this stringer clip is relatively easy to install, and one size fits a large number of stringer sizes and shapes, this stringer clip is primarily suitable for light attachments because it tends to loosen under heavy loading. In addition, the flexible strap attachment does not fill the middle channel of the stringer webs, leaving it open. As such, the stringer can be pinched and distorted if the strap is pulled too tightly and/or if the attached structures are relatively heavy. This distortion of the stringer can have a negative impact on the structural integrity of the aircraft and, therefore, is undesirable.